Chemical mechanical planarization, also known as chemical mechanical polishing or CMP, is a technique used to planarize the top surface of an in-process semiconductor wafer or other substrates, such as optical, magnetic type of substrates in preparation of subsequent steps or for selectively removing material. The technique employs a slurry that can have corrosive and abrasive properties in conjunction with a polishing pad.
The rapid advances in semiconductor technology has seen the advent of very large scale integration (VLSI) and ultra large scale integration (ULSI) circuits resulting in the packing of many more devices in smaller area in areas in a semiconductor substrate. The greater device densities require a great degree of both polish and planarity to permit the higher resolution lithographic processes required to form the greater number of devices having smaller feature incorporated in current designs. Moreover, copper, because of its low resistance is increasingly being used as interconnects. Conventionally, etching techniques are used to planarize conductive (metal) and insulator surfaces. However, certain metals, desirable for their advantageous properties when used as interconnect (Au, Ag, Cu) are not readily amenable to etching, thus the need for CMP processes.
Typically, CMP is a dynamic process involving cyclic motion of both the polishing pad and the workpiece. CMP combines the chemical conversion of the surface layer removed, wit the mechanical removal of the conversion product. Ideally, the conversion product is soft, facilitating high polishing rates. An advantage of the soft polishing pad is low defect density of the polished wafer and good within-wafer uniformity. However, soft CMP pads suffer from a short pad life requiring replacement after about 50 wafers. Further, during the polishing cycle energy is transmitted to the pad. A portion of this energy is dissipated inside the pad as heat, and the remaining portion is stored in the pad and subsequently released as elastic energy during the polishing cycle. The latter is believed to contribute to the phenomenon of dishing of metal features and oxide erosion. While it is generally, known that prevention of dishing requires a stiffer pad, this type of pad increases the number and density of surface scratches and defects.
Therefore, a need continues to exist for CMP pads that provide good removal rates, good within wafer (WIW) and within die (WID) uniformities, low dishing and/or erosion, reduced scratching, lower conditioning requirements and prolonged pad life.